An early clinical trial of a
breast-cancer vaccine developed at Washington University School of Medicine has
shown promise in a small study. Researchers found that the vaccine triggered
patients’ immune systems to attack tumor cells and helped slow the cancer’s
progression.

The vaccine works by causing the immune
system to home in on a protein called mammaglobin-A, which is found almost
exclusively in breast tissue. Though researchers don’t know what role this
protein plays in healthy breast tissue, they do know that breast tumors express
it at abnormally high levels. The vaccine prompts certain white blood cells to
seek out and destroy cells carrying the mammaglobin-A protein.

The study included 14 patients with
metastatic breast cancer that expressed mammaglobin-A. Because it was a phase I
trial, the study was designed to look primarily at the vaccine’s safety.
Researchers found that participants experienced few side effects, reporting
eight events classified as mild or moderate, including rash, tenderness at the
vaccination site and mild flu-like symptoms. No severe or life-threatening side
effects occurred.

Based on the results of the phase I
study, researchers are now planning a larger clinical trial to test the vaccine
in patients with newly diagnosed breast-cancer, who, in theory, should have more
robust immune systems than patients who already have had extensive cancer
therapy.

“If we give the vaccine to patients at
the beginning of treatment, their immune systems should not be compromised like
they are in patients with metastatic disease,” says William Gillanders, MD, a
Washington University breast-cancer surgeon at Siteman Cancer Center and the
leader of the phase I trial. “Now that we have good evidence that the vaccine is
safe, we think testing it in newly diagnosed patients will give us a better idea
of the effectiveness of the therapy.”